feat: Implement document upload functionality and update agent profile edit screen UI with a new back icon.

lib/features/profile/data/profile_repository.dart

@@ -96,6 +96,30 @@ class ProfileRepository {
     }
   }
 
+  /// Get presigned upload URL for documents.
+  /// Returns { uploadUrl: String, key: String, publicUrl: String }
+  Future<Map<String, String>> getDocumentUploadUrl(
+      String fileName, String contentType) async {
+    try {
+      final response = await _dio.post('/upload/presigned-url', data: {
+        'filename': fileName,
+        'contentType': contentType,
+      });
+      final data = response.data['data'] as Map<String, dynamic>;
+      return {
+        'uploadUrl': data['uploadUrl'] as String,
+        'key': data['key'] as String,
+        'publicUrl': (data['publicUrl'] ?? data['key'] ?? '') as String,
+      };
+    } on DioException catch (e) {
+      if (e.error is ApiException) throw e.error as ApiException;
+      throw ApiException(
+        message: e.message ?? 'Failed to get document upload URL',
+        statusCode: e.response?.statusCode,
+      );
+    }
+  }
+
   /// Delete avatar from S3: DELETE /upload/{encodedKey}
   Future<void> deleteAvatar(String key) async {
     try {